“How much could the person you love change, and still remain the same person to whom you'd made your promise? We don't expect our lovers to remain the same over the course of a long relationship. In fact, if you're married at sixty-five to the same person you married when you were twenty, your marriage has probably failed. But there are changes, over time, that spell doom for a marriage, although exactly what these are, and to what degree, varies from couple to couple. For some people, vast changes over time make no difference to the fundamental sense of devotion one soul has for another. But for others, relatively small changes can push things to the breaking point: gaining or losing weight, gaining or losing faith, gaining or losing wealth. How does any relationship survive in the end, when change is the only constant?”